I'm not necessarily opposed to this but just wondered if the increase the height by 23m as proposed what effect will this have on bushland further up the valley eg say the Kedumba valley. Would it be under water for some or all of the year?

Could this also be construed as "direct action" in response to a changing climate?

On 1/03/2013 maxdacat wrote:>I'm not necessarily opposed to this but just wondered if the increase the>height by 23m as proposed what effect will this have on bushland further>up the valley eg say the Kedumba valley. Would it be under water for some>or all of the year?>(snip)

If you were to go to the furthest end of storage away from the wall, you would notice a 'high water line' where the vegetation changes from 'normal' to almost nonexistent, due to regular inundation below it.
Add 23 m of height to that line and extrapolate further back into the valley headwaters to find your new high water line ...

Regarding period of inundation, I believe that if you obtained storage water level (SWL) data for that site for say the last 20 or 30 years (or longer), that you would notice a cyclic variation in it based on season/rainfall/usage and could deduce a mean inundation time for any given WL.
Without quantifying this, I guess that a couple of months a year might be a reasonable expectation of full supply levels being maintained (when possible*), and that is sufficient to kill off vegetation below that WL.
(*This does not take into account other storage purposes like flood mitigation, extended drought, etc).

Storages are interesting ecological dis/benefit items, as there are often a range of water quality issues (eutrophication, thermal pollution, algal blooms, etc) attached as well.

On 1/03/2013 maxdacat wrote:>>Could this also be construed as "direct action" in response to a changing>climate?>

No, it is 'direct action' of Penrith City Council, Hawkesbury City Council and others that want more land 'flood-proofed' so as to make them more appealing to build housing developments on - to simply keep Sydney rolling in cash. This may not work.

If it were for flood mitgation then that is what it would be used for , ie store the inflow from extreme rain whilst not dicharging to cause major flooding down stream , it would drop back to full supply as quckly as possible to enable the next flood to be mitigated . So effect on valley would probably be minimal as inundation would only be days or weeks at the most . As changing weather pattern is making extremes greater probably not a bad idea . Think what would have happened to Brisbane without the Wivenhoe dam going up from 100 % (water supply ) to 190% flood mitigation . The arguments there were the dam should have been well below 100 % before the flood and intial releases higher than they actually were but the dam certainly saved brisbane from a much bigger flood as at all times the releases were controlled according to the operating "rules "

On 1/03/2013 lacto wrote:>If it were for flood mitgation then that is what it would be used for , ie store the inflow from extreme rain whilst not dicharging to cause major flooding down stream , it would drop back to full supply as quckly as possible to enable the next flood to be mitigated .

This assumes a designated ‘full supply level’ which is actually less than full capacity of the dam involved. That situation can, and does, occur. In fact the 'operating rules' can change depending on season and longer term climatic trends happening from time to time, not to mention politics!

>So effect on valley would probably be minimal as inundation would only be days or weeks at the most . As changing weather pattern is making extremes greater probably not a bad idea . Think what would have happened to Brisbane without the Wivenhoe dam going up from 100 % (water supply ) to 190% flood mitigation .

That figure sounds suspiciously high to me, and if we are using the same terminology*, then an unlikely thing to be able to achieve. It depends entirely on the nature of a gated structure and the event in question. From my understanding, a figure higher than 110% full capacity level is doubtful.
(*You may be referring to a designed flood capacity, in which case the 'full' water supply level is sometimes lowered accordingly. This is different to a designed flood surcharge, which is achieved over and above whatever the full supply level is set at, even if this also coincides with full dam capacity.)

>The arguments there were the dam should have been well below 100 % before the flood and intial releases higher than they actually were but the dam certainly saved brisbane from a much bigger flood as at all times the releases were controlled according to the operating "rules "

The operation of that dam at that time has since been the subject of intense scrutiny. I feel for the Operators during that event, as they were the workers likely scape-goated by ‘managers’ with vested interests in protecting their own skins; ... and all bought about by insurance claims by people who have houses built on flood prone land regardless of any infrastructure/operation of same.

There are some interesting stats on Warragamba Dam here on Wikipedia, but nothing pertaining to operational rules, current or otherwise.

I think the the 1 in a 100 year level is old hat now. I think that all main dams in Aus are now heading for 1 in a 1000 year as the standard. Insurance is demanding this as the level. We owned an accommodation business in Tas that hosted a team that were raising the heights on nearby dams and that was what they told us was happening.

IIRC Wivenhoe full or 100% means water to the spillway, ie if the gates were open water flows out. The 190% meant as close to the top of the dam wall they dared to go without chancing the integrity of the wall itself. I gather this changes depending on the construction of the wall.

The amount of water in Wivenhoe nearly doubled in a very short period, in was flowing in faster than it could be let out the gates. I remember hearing the level at the dam wall was rising a metre an hour (or something crazy) at some point.

James is right 100 is level to the gated spillway and as gated the flow is controllable but once over this water flows over an untrolled spillway hence the statement that fotunately the flows were" safe "as above 190% the flow couldn't be controlled . One fo the problems facing controllers that if the release more water than flowing in then they create the flood and would be liable for any damage it caused even if later flows were far in excess of the intial flood . Flood mitigation should never release more water than is flowing in and releases the excess after the peak has passed but at a greater flow than the inflow .
If warragamba "capacity " were to be increased it is unlikely that the normal storage would be increased as that would reduce the flood mitigation ability and open the operators liable for flood damage . All major dams are undergoing flood capacity to 1 in 1000 (or 10000 )year rain events

Flood mitigation is a very interesting idea. The very reason people inhabit flood plains is or was the flooding which created the level, rich plains in the first place. My mate in walgett was complaining about flooding last year. I pointed out that's why his farm is productive; and guess what the next season was the best he'd ever had

This was looked at 20 years ago and after a conservation battle rejected. It would basically wipe out the lower Kowmung River - perhaps the best remaining wild river in NSW. The river now lies in a world heritage area - and I would have thought that it would be safe from destruction. To put this in terms that climbers might appreciate - it would be as though My Arapiles was completely quarried and turned into road fill.

Raising the storage and raising the flood mitigation are 2 completely separate senarios increasing storage would devastate wereas flood mitigation may innundate for very short periods from a few hours to maybe a week with aprobability of 1 in 100+ years .
Eppalock on the campapse held back 125% of its capacity for a week or so a few years ago . The water banks up to flow over a spillway and is totally controlled by inflows and the ability to exit the spillway. Lake Eildon has recently been up graded to the new standards its capacity is 3.3 Million ML but is designed to hold another 14.1 metres of water which is 1.9 Million ML if it doesnt flood anymore area in reallity probably 2.5 Ml or 70+ % of capacity . the comparison to Arapiles is nonsense .
The problem HAS TO BE addressed as huge suburban development is already impacted by foods with continuous new development and the new standards would throw liability back on the government if the upgrades arent carried out .

On 2/03/2013 lacto wrote:>Raising the storage and raising the flood mitigation are 2 completely separate>senarios increasing storage would devastate wereas flood mitigation may>innundate for very short periods from a few hours to maybe a week with>aprobability of 1 in 100+ years .

Hey Lacto, just wondering if you have any inside knowledge on this? The consultants report linked further up this thread clearly has an agenda and that is to support additional flood mitigation capability in Warragamba Dam. The section in the report about the impact on the upstream environment may not be the whole story. As you note this depends on how quickly the water is released following the flood peak. This in turn will depend on design and policy. Is there a definitive preferred design out there? Until there is it may be a bit premature to conclude upstream impacts are negligiable.

>The problem HAS TO BE addressed as huge suburban development is already>impacted by foods with continuous new development and the new standards>would throw liability back on the government if the upgrades arent carried>out .

I wish I could disagree with you. Inappropriate development has been going on the Hawkesbury-Nepean flood plain since Governor Macquarie was punching on with the squatter aristocracy in the early 19th century.

DaveN alluded to the last time a similar proposal came up in the 1990s. This is only my opinion only but while the conservation campaign at the time may have contributed to the scrapping of the flood mitigation component of the dam upgrade, the major factor for not going ahead with it was cost.

That cost benefit equation has changed drastically since. There are a bunch reasons for this such as an increase in government insurance costs following natural disasters in Victoria and Qld, changes in flood risk modelling predicting more frequent severe flooding, and the uncertainty over the impact of climate change.

So to answer the OP- Some good, some bad depending on your point of view, but sadly inevitable.

I have no inside knowledge at all , but a reasonable understanding of the need to up grade the ability of dams to cope with huge rainfall events as well as earthquakes . Eildon was done and basically paid for by the irrigators by losing 20% of their sales water right new flood capability is 14.1 meters above full supply level , interestingly the record inflow occured in 1993 500mm of rain and inflows peaked at 160, 000 Ml a day or roughly 1 metre water rise . If the dam were to increase for flood mitigation it would need to drop down very quickly in case of another such event . Melbourne City area had 2 100 to 150 year probability rain events 3 days apart , water was nearly 1 metre deep flowing down Elizabeth St . Whether climate change or just the on going records the rainfall events seem to be getting larger and more frequent remember the heaviest rainfall and greatest drought statistically have yet to occur . I doubt that warragamba dam could have an increase in capacity as well as the flood mitigation

> Up to a million additional vehicle movements per day in the Hawkesbury-Nepean valley, causing traffic congestion, air pollution and resulting health problems in the whole of western Sydney

1 000 000 additional vehicles? Really? If so, when - 50 years hence?

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> A huge increase in run-off and sewage discharge that will cause even worse deterioration of water quality in the Hawkesbury-Nepean River.

Two STP's discharge treated effluent into the Nepean below Warragamba. Penrith and the vast majority of all of the City of the Blue Mountains. The latter comes from the Winmalee STP only, and I once did a tour through this place, where I was told by a professional that the treated discharge is better to drink than your tap water.
Wouldn't this healthy discharge assist with river quality?

Huge increase in run-off? Let us promote and lobby for storm-water harvesting. Now.

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> Loss of rich agricultural land to urban expansion and destruction of fisheries, including the major oyster farming industry.

I have kayaked both Mullet Creek and Patonga Creek in the past month - and seen near-derelict oyster racks. Not certain what is going on here, though flooding rains may have shifted the many racks. Nylon baskets of oysters have been seen washed ashore in both creeks. Is enough maintenance by the agriculturist being done?

I undertook a large tour of an oyster farming operation 2 years ago. We toured downstream, from Mooney Mooney along the Hawkesbury River to Broken Bay. Mooney Mooney Ck (adjacent to the F3 motorway) is over 150km from the Warragamba River junction.
Isn't of more immediate concern, the 'sport' of Power Boating gives rise to swash, causing bank erosion? These high-speed craft may be planing, but how many are entered in this weekends (May 5) annual Bridge to Bridge race. The river has extraordinarily few berms to dissipate the water energy, leading to sedimentation and hence depleted fish stocks. Back it up with the high-profile long-distance water-ski version in November/October, and the river is seen never to have a chance to recover already.

There was temporary loss of agricultural land on the Richmond Lowlands the most recent time Warragamba dam spilt. Raising the dam wall would have prevented this. The rains filled Lake Burragorang faster than the release could cope, and hence the spillway came into play.

I have seen in the last 10 years loss of agricultural land due to expansion of the Penrith Lakes Scheme displacing dairy farms along the (old) Castlereagh Road, as well as a Kennards(?) storage facility where there was another dairy farm at the corner of Coreen Avenue and Castlereagh Rd. The new Castlereagh Rd also took away agricultural lands, as did, ironically to the original gist of this thread, the artificial river of Penrith White-water Stadium.